Well, for me, both of my programming hobby projects stem from a single dream I have been having for years: Building a virtual reality according to my dreams and wishes. Well, it probably started with 8th grader syndrome, but that doesn't matter to me anymore, today :D
Apart from them, I have a few more projects I want to work on more, but have serious time issues at the moment (24h/day is not enough). They mainly stem from needs and the wish to have some cool stuff to show off
Other ideas came and went mainly with the help of fun evenings and a few beers, but most of them didn't interest me enough to actually work on them.